Tewephone numbering pwan

A tewephone numbering pwan is a type of numbering scheme used in tewecommunication to assign tewephone numbers to subscriber tewephones or oder tewephony endpoints.[1] Tewephone numbers are de addresses of participants in a tewephone network, reachabwe by a system of destination code routing. Tewephone numbering pwans are defined in each of administrative regions of de pubwic switched tewephone network (PSTN) and dey are awso present in private tewephone networks. For pubwic number systems, geographic wocation pways a rowe in de seqwence of numbers assigned to each tewephone subscriber.

Numbering pwans may fowwow a variety of design strategies which have often arisen from de historicaw evowution of individuaw tewephone networks and wocaw reqwirements. A broad division is commonwy recognized, distinguishing open numbering pwans and cwosed numbering pwans[discuss]. Many numbering pwans subdivide deir territory of service into geographic regions designated by a prefix, often cawwed an area code or city code, which is a set of digits forming de most-significant part of de diawing seqwence to reach a tewephone subscriber.

The Internationaw Tewecommunication Union (ITU) has estabwished a comprehensive numbering pwan, designated E.164, for uniform interoperabiwity of de networks of its member state or regionaw administrations. It is an open numbering pwan, however, imposing a maximum wengf of 15 digits to tewephone numbers. The standard defines a country cawwing code (country code) for each state or region which is prefixed to each nationaw numbering pwan tewephone number for internationaw destination routing.

Private numbering pwans exist in tewephone networks dat are privatewy operated in an enterprise or organizationaw campus. Such systems may be supported by a private branch exchange (PBX), which controws internaw communications between tewephone extensions.

In contrast to numbering pwans, which determine tewephone numbers assigned to subscriber stations, diawing pwans estabwish de customer diawing procedures, i.e. de seqwence of digits reqwired to reach a destination, uh-hah-hah-hah. Even in cwosed numbering pwans, it is not awways necessary to diaw aww digits of a number. For exampwe, an area code may often be omitted when de destination is in de same area as de cawwing station, uh-hah-hah-hah.

The Norf American Numbering Pwan is a cwosed numbering pwan,[2][3] which prescribes ten digits for each compwete destination routing code, incwuding a dree-digit area code fowwowed by a dree-digit exchange and den four more digits. In de United States and Canada, area codes were first awwocated in 1947. In some warge cities dey were used soon after as operator routing codes for connecting wong-distance tewephone cawws between toww switching centers.[4] The first customer-diawed wong-distance cawws were possibwe in Engwewood, NJ in 1951. By ca. 1966, de system was impwemented fuwwy in bof countries[5] and users of de tewephone system needed to wearn deir own area code. The Beww System organized de numbering pwan to minimize de cost of providing automatic diawing to warge popuwation centers, as cawws dat crossed area code boundaries were reqwired to be switched by speciaw toww switching systems. For exampwe, geographic areas were designed so dat tributary routes were pwaced into de same area as de major toww center.[6]

Due to a technicaw wimitation of de numbering pwan[citation needed], states dat were anticipated to reqwire more dan about 500 centraw offices were spwit into muwtipwe areas, each receiving a code wif de middwe digit being 1. On de oder hand, area codes dat covered an entire state had de digit 0 in de middwe. In contrast to de area code, de second digit of de dree-digit exchange code was never 0 or 1, dus affording a simpwe ruwe for recognition of wheder a user was diawing a fuww ten-digit tewephone number or merewy diawing widin de wocaw area code using seven-digit diawing. Toww operators were abwe to differentiate between de two types of areas from de middwe digit of de area code when a routing operator had to be consuwted.[7]

By de 1990s, de ewectromechanicaw centraw office switches were repwaced wif ewectronic switching system (ESS) eqwipment and de previous area code wogic was no wonger necessary. The demand for tewephone numbers was increasing rapidwy, and de remaining n0n and n1n combinations were insufficient to sustain growf. This area code scheme was abandoned, wif de resuwt dat area codes and centraw office codes couwd not necessariwy be automaticawwy distinguished by de switching eqwipment. The sowution was to reqwire de diawing of a preceding 1 for cawws across area codes, in which case de eqwipment expected 10 more digits. If de first digit diawed was not a "1", onwy 7 digits were expected and de area code was inferred from de originating subscriber's area code. For a short whiwe, in some area codes, one couwd enter de fuww 11 digits for a caww widin deir own neighborhood or just enter de wast 7 digits, and de caww wouwd be routed and biwwed identicawwy.

The rising popuwarity of fax machines and pagers reqwired far more tewephone numbers dan were anticipated in de design of de numbering system. As a remedy, de restrictions on de format of area codes were eased. Since 1995, over 380 new area codes were added to de Norf American Numbering Pwan, uh-hah-hah-hah. Some areas used area code spwits, by which an existing numbering pwan area (NPA) was spwit into muwtipwe divisions each assigned a new area code. Thus, many businesses were reqwired to reprint business stationery, catawogs, and directories. Area code spwits were often contested as to which area couwd keep de existing code, which usuawwy feww to de wargest city. For exampwe, 305 was spwit in 1995, and had served bof de Miami and Fort Lauderdawe area. Dade County (Miami-Dade) kept 305 and Broward County (Fort Lauderdawe area) had to change to 954. Anoder medod was using area code overways, which avoided renumbering existing stations. An overway is a new area code dat covers de same geographicaw area as an existing code. Over 75 overways have been introduced since 1995.[8]

Area code overways invariabwy reqwire ten-digit diawing of tewephone numbers in de numbering pwan area. Internet tewephony services are not tied to physicaw wocations and area codes often no wonger correspond to de physicaw wocation of de provider, nor de subscriber.[9]

Numbering pwans awso decide on de routing of Signawing System 7 (SS7) signawing messages as part of de Gwobaw Titwe. In pubwic wand mobiwe networks, de E.212 numbering pwan is used for subscriber identities, e.g., stored in de GSMSIM, whiwe E.214 is used for routing database qweries across PSTN networks. In generaw, de structure of tewephone numbers issued widin a nationaw tewephone numbering pwan fowwows bof de internationaw formats and de nationaw standards. Widin de internationaw system administered by de ITU, each nationaw pwan has a uniqwe country code.

Widin de nationaw numbering pwan, a compwete destination tewephone number is composed of an area code and a subscriber tewephone number. The subscriber number is de number assigned to a wine connected to customer eqwipment. It must be diawed in its entirety.[citation needed] The first few digits of de subscriber number typicawwy indicate smawwer geographicaw areas or individuaw tewephone exchanges. In mobiwe networks dey may indicate de network provider. Cawwers in a given area or country usuawwy do not need to incwude de particuwar area prefixes when diawing widin de same area. Devices dat diaw tewephone numbers automaticawwy may incwude de fuww number wif area and access codes.

Country codes are necessary onwy when diawing tewephone numbers in oder countries dan de originating tewephone. These are diawed before de nationaw tewephone number. By convention, internationaw tewephone numbers are indicated by prefixing de country code wif a pwus sign (+), which is meant to indicate dat de subscriber must diaw de internationaw diawing prefix in de country from which de caww is pwaced. For exampwe, de internationaw diawing prefix or access code in aww NANP countries is 011, whiwe it is 00 in most European countries. On GSM networks, + is an actuaw keypad code dat may be recognized automaticawwy by de network carrier in pwace of de internationaw access code.

Many tewephone numbering pwans are structured based on divisions into geographic areas of de service territory. Each area identified in de pwan is assigned a numeric routing code. This concept was first devewoped for Operator Toww Diawing of de Beww System in de earwy 1940s, which preceded de Norf American Numbering Pwan (NANP) of 1947.[10] The system divided de Norf American service territories into numbering pwan areas (NPAs), and cawwed de numericaw prefix de numbering pwan area code, which became known in a short-form as area code. The area code is prefixed to each tewephone number assigned.

Nationaw tewecommunication audorities use various formats and diawing ruwes for area codes. In de initiaw design of de NANP, de dree-digit format was NBX, where N couwd be any digit from 2 drough 9, B eider 0 §or 1, and X any digit, awdough no area code ended in 0 untiw de code 800 was introduced for toww-free service. The pattern of assignment to geographicaw areas avoided nearby areas having simiwar area codes, to avoid confusion and misdiawed numbers. In 1995, during de expansion of area codes de center-digit ruwe was rewaxed, defining it as any digit except 9. 9 as de middwe digit of an NPA is reserved in case de dree-digit area code poow is exhausted and has to be augmented to four digits.

Some countries, such as Uruguay, have merged variabwe-wengf area codes and tewephone numbers into fixed-wengf numbers dat must awways be diawed independentwy of wocation, uh-hah-hah-hah. In such cwosed diawing pwans, awso having a cwosed numbering pwan, de area code is formawwy not distinguished in de tewephone number. In de UK, area codes were first known as subscriber trunk diawwing (STD) codes. Depending on wocaw diawing pwans, dey are often necessary onwy when diawed from outside de code area or from mobiwe phones. In Norf America ten-digit diawing is reqwired in areas wif overway pwans.

The strict correwation of a tewephone to a geographicaw area has been broken by technicaw advances, especiawwy VoIP service.[11]

The area code is usuawwy preceded in de diawing seqwence by eider de nationaw access code ("0" for many countries, "1" in USA and Canada) or de internationaw access code and country code. However, dis is not awways de case, especiawwy when 10-digit diawing is used. For exampwe, in Montreaw, where area codes 514, 438, 450 and 579 are in use, users diaw 10-digit numbers (e.g., 514 555 1234), diawing a 1 before dis resuwts in a recording advising not to diaw a 1 as it is a wocaw caww. For non-geographic numbers, as weww as mobiwe tewephones outside of de Norf American Numbering Pwan area, de area code does not correwate to a particuwar geographic area. However, untiw de 1990s, some areas in de United States and Canada reqwired de use of a 1 before diawing a 7-digit number widin de same area code if de caww was beyond de wocaw toww-free area, indicating dat de cawwer wished to make what was referred to as a toww caww.

Area codes are often qwoted by incwuding de nationaw access code. For exampwe, a number in London shouwd be wisted as 020 7946 0321. Users must correctwy interpret de 020 as de code for London, uh-hah-hah-hah. If dey caww from anoder station widin London, dey may merewy diaw 7946 0321, or if diawing from anoder country, de initiaw 0 shouwd be omitted after de country code: +44 20 7946 0321.

In countries oder dan de United States and Canada, de area codes generawwy determine de cost of a caww, and cawws widin an area code and often a smaww group of adjacent or overwapping area codes are normawwy charged at a wower rate dan outside de area code. This is not necessariwy de case in de United States or Canada, where area codes cover a sufficientwy warge territory dat different rates wiww appwy widin de same area code and toww rates may be determined by de distance between rate centers. The area code and centraw office prefix (NPA-NXX) define de rate center, which is assigned geographic coordinates V&H. Each rate center has a wocaw cawwing pwan dat determines which oder rate centers are a wocaw caww, regardwess of distance, and oder towws are based on de tariff distance between de two rate centers, using dis formuwa: (V1−V2)2+(H1−H2)210{\dispwaystywe {\sqrt {\frac {(V1-V2)^{2}+(H1-H2)^{2}}{10}}}}

Therefore, cawws between nearby rate centers in different area codes may be cheaper dan cawws to more distant rate centers in de same area code. Rates are set in zones of 0-6 mi, 6-12 mi, and so on, wif dese bands determined on a state-by-state basis for intrastate cawws (cawws widin de same state) and determined by federaw reguwation for interstate cawws (cawws which cross a state wine). As a specific exampwe, cawwers in de Fawws Church, Virginia, rate center, which is officiawwy named "Washington Zone 17, VA"—exampwe numbers begin wif 703-534, V=5636, H=1600, may make unmetered wocaw cawws to 31 oder nearby rate centers in Virginia, Marywand, and de District of Cowumbia in area codes 703, 571, 202, 301, and 240, whiwe cawws to distant wocations in 703, such as Manassas and Haymarket, VA, are charged as wong distance.

Cawws widin a state [reguwated by dat state's pubwic utiwities commission] are often higher dan rates to caww more distant wocations in some oder state [reguwated by de Federaw Communications Commission]. The partiaw dereguwation and introduction of competition for wong-distance phone services has estabwished oder medods of determining caww pricing dat do not necessariwy fowwow de traditionaw modew. Each year, more customers switch to a fixed rate, "aww-you-can-diaw" pwan covering de state, de United States, or aww Norf America generawwy (as of May 2008 and excwusive of taxes) for approximatewy $30 per monf. Competition wif cabwe tewephony and Voice over Internet Protocow services has hewped drive de cost of service down for residentiaw and business customers.

Speciaw area codes are generawwy used for free, premium-rate, mobiwe phone systems (in countries where de mobiwe phone system is "cawwer pays") and oder speciaw-rate numbers. There are, however, some exceptions: in some countries, such as Egypt, cawws are charged at de same rate regardwess of area and in oders, such as de UK, an area code is occasionawwy treated as two areas wif different rates.

Landwine tewephony operators in United States maintain a separate pricing structure for IntraLATA phone cawws, awso known as "wocaw wong distance". The tariff rate for dese cawws to nearby areas may greatwy exceed de rates for wong distance domestic cawws dat are on de oder side of de continent.[12]

A diaw pwan estabwishes de expected seqwence of digits diawed on subscriber premises eqwipment, such as tewephones, in private branch exchange (PBX) systems, or in oder tewephone switches to effect access to de tewephone networks for de routing of tewephone cawws, or to effect or activate specific service features by de wocaw tewephone company, such as 311 or 411 service.

A variety of diaw pwans may exist widin a numbering pwan and dese often depend on de network architecture of de wocaw tewephone operating company.

Widin de Norf American Numbering Pwan, de administration defines standard and permissive diawing pwans, specifying de number of mandatory digits to be diawed for wocaw cawws widin de area code, as weww as awternate, optionaw seqwences, such as adding de trunk code 1 before de tewephone number.

Despite a cwosed numbering pwan, different diawing procedures exist in many of de territories for wocaw and wong distance tewephone cawws. This means dat to caww anoder number widin de same city or area, cawwers need to diaw onwy a subset of de fuww tewephone number. For exampwe, in de NANP, onwy de 7-digit number may need to be diawed, but for cawws outside de area, de fuww number incwuding de area code is reqwired. In dese situations, de ITU-T Recommendation E.123 suggests to wist de area code in parendeses, signifying dat in some cases de area code is optionaw or is not reqwired. Typicawwy de area code is prefixed by a domestic trunk access code (usuawwy 0) when diawing from inside a country, but is not necessary when cawwing from oder countries, but dere are exceptions, such as for Itawian wand wines.

The pwus character (+) in de markup signifies dat de fowwowing digits are de country code, in dis case 61. Some phones, especiawwy mobiwe tewephones, awwow de + to be entered directwy. For oder devices de user must repwace de + wif de internationaw access code for deir current wocation, uh-hah-hah-hah.

New Zeawand has a speciaw case diaw pwan, uh-hah-hah-hah. Whiwe most nations reqwire de area code to be diawed onwy if it is different, in New Zeawand, one needs to diaw de area code if de phone is outside de wocaw cawwing area. For exampwe, de town of Waikouaiti is in de Dunedin City Counciw jurisdiction, and has phone numbers (03) 465 7xxx. To caww de city counciw in centraw Dunedin (03) 477 4000, residents must diaw de number in fuww incwuding de area code even dough de area code is de same, as Waikouaiti and Dunedin wie in different wocaw cawwing areas (Pawmerston and Dunedin respectivewy)[13]

In de United States, Canada, and oder countries or territories using de Norf American Numbering Pwan (NANP), de internationaw trunk access code is 1, which is awso de country cawwing code. The same ruwe awso appwies in many parts of de NANP, incwuding aww areas of Canada dat stiww have variabwe-wengf diaw pwan, uh-hah-hah-hah. This is not universaw, as dere are wocations widin de United States dat awwow wong distance cawws widin de same area code to be diawed as seven digits. In Canada, de domestic trunk code (wong distance access code) must awso be diawed awong wif de area code for wong distance cawws even widin de same area code. For exampwe, to caww a number in Regina in area code 306 (Regina and de rest of de province of Saskatchewan are awso served by de overway code 639):

1 510 xxx xxxx — wocaw or wong-distance outside of 510 but widin de U.S., Canada, and oder countries in de NANP. 1 is de wong-distance trunk code.

1 510 xxx xxxx — outside de NANP. 1 is de country code for de U.S.

However, in parts of Norf America, especiawwy where a new area code overways an owder area code, diawing de area code, or 1 and de area code, is reqwired even for wocaw cawws. Diawing from mobiwe phones is different in de U.S., as de trunk code is not necessary, awdough it is stiww necessary for cawwing aww wong distance numbers from a mobiwe phone in Canada. Most mobiwe phones can be configured to automaticawwy add a freqwentwy-cawwed area code as a prefix, awwowing cawws widin de desired area to be diawed by de user as seven-digit numbers, dough sent by de phone as 10-digit numbers.

In some parts of de United States, especiawwy nordeastern states such as Pennsywvania served by Verizon Communications, de fuww 10-digit number must be diawed. If de caww is not wocaw, de caww wiww faiw unwess de diawed number is preceded by digit 1. Thus:

610 xxx xxxx — wocaw cawws widin de 610 area code and its overway (484), as weww as cawws to or from de neighboring 215 area code and its overway, 267. Area code is reqwired; one of two compwetion options for mobiwe phones widin de U.S.

1 610 xxx xxxx — cawws from numbers outside de 610/484 and 215/267 area codes; second of two compwetion options for mobiwe phones widin de U.S.

In Cawifornia and New York, because of de existence of bof overway area codes (where an area code must be diawed for every caww) and non-overway area codes (where an area code is diawed onwy for cawws outside de subscriber's home area code), "permissive home area code diawing" of 1 + de area code widin de same area code, even if no area code is reqwired, has been permitted since de mid-2000s (decade). For exampwe, in de 213 area code (a non-overway area code), cawws may be diawed as 7 digits (XXX-XXXX) or 1-213 + 7 digits. The manner in which a caww is diawed does not affect de biwwing of de caww. This "permissive home area code diawing" hewps maintain uniformity and ewiminates confusion given de different types of area code rewief dat has made Cawifornia de nation's most "area code" intensive State. Unwike oder states wif overway area codes (Texas, Marywand, Fworida and Pennsywvania and oders), de Cawifornia Pubwic Utiwities Commission and de New York State Pubwic Service Commission maintain two different diaw pwans: Landwines must diaw 1 + area code whenever an Area Code is part of de diawed digits whiwe cewwphone users can omit de "1" and just diaw 10 digits.

Many organizations have private branch exchange systems which permit diawing de access digit(s) for an outside wine (usuawwy 9 or 8), a "1" and finawwy de wocaw area code and xxx xxxx in areas widout overways. This aspect is unintentionawwy hewpfuw for empwoyees who reside in one area code and work in an area code wif one, two, or dree adjacent area codes. 1+ diawing to any area code by an empwoyee can be done qwickwy, wif aww exceptions processed by de private branch exchange and passed onto de pubwic switched tewephone network.

In smaww countries or areas, de fuww tewephone number is used for aww cawws, even in de same area. This has traditionawwy been de case in smaww countries and territories where area codes have not been reqwired. However, dere has been a trend in many countries towards making aww numbers a standard wengf, and incorporating de area code into de subscriber's number. This usuawwy makes de use of a trunk code obsowete. For exampwe, to caww Oswo in Norway before 1992, it was necessary to diaw:

Whiwe diawing of fuww nationaw numbers takes wonger dan a wocaw number widout de area code, de increased use of phones dat can store numbers means dat dis is of decreasing importance. It awso makes it easier to dispway numbers in de internationaw format, as no trunk code is reqwired—hence a number in Prague, Czech Repubwic, can now be dispwayed as:

The E.164 standard of de Internationaw Tewecommunications Union is an internationaw numbering pwan and estabwishes a country cawwing code (country code) for each member organization, uh-hah-hah-hah. Country codes are prefixes to nationaw tewephone numbers dat denote caww routing to de network of a subordinate number pwan administration, typicawwy a country, or group of countries wif a uniform numbering pwan, such as de NANP. E.164 permits a maximum wengf of 15 digits for de compwete internationaw phone number consisting of de country code, de nationaw routing code (area code), and de subscriber number. E.164 does not define regionaw numbering pwans, however, it does provide recommendations for new impwementations and uniform representation of aww tewephone numbers.

Widin de system of country cawwing codes, de ITU has defined certain prefixes for speciaw services and assigns such codes for independent internationaw networks, such as satewwite systems, spanning beyond de scope of regionaw audorities.

The numbering pwan indicator (NPI) is a number which is defined in de ITU standard Q.713, paragraph 3.4.2.3.3, indicating de numbering pwan of de attached tewephone number. NPIs can be found in Signawwing Connection Controw Part (SCCP) and short message service (SMS) messages. As of 2004[update], de fowwowing numbering pwans and deir respective numbering pwan indicator vawues have been defined:

Like a pubwic tewecommunications network, a private tewephone network in an enterprise or widin an organizationaw campus may impwement a private numbering pwan for de instawwed base of tewephones for internaw communication, uh-hah-hah-hah. Such networks operate a private switching system or a private branch exchange (PBX) widin de network. The internaw numbers assigned are often cawwed extension numbers, as de internaw numbering pwan extends an officiaw, pubwished main access number for de entire network. A cawwer from widin de network onwy diaws de extension number assigned to anoder internaw destination tewephone.

A private numbering pwan provides de convenience of mapping station tewephone numbers to oder commonwy used numbering schemes in an enterprise. For exampwe, station numbers may be assigned as de room number of a hotew or hospitaw. Station numbers may awso be strategicawwy mapped to certain keywords composed from de wetters on de tewephone diaw, such as 4357 (hewp) to reach a hewp desk.

The internaw number assignments may be independent of any direct inward diawing (DID) services provided by externaw tewecommunication vendors. For numbers widout DID access, de internaw switch reways externawwy originated cawws via an operator, an automated attendant or an ewectronic interactive voice response system. Tewephone numbers for users widin such systems are often pubwished by suffixing de officiaw tewephone number wif de extension number, e.g., 1-800-555-0001 x2055.

Some systems may automaticawwy map a warge bwock of DID numbers (differing onwy in a traiwing seqwence of digits) to a corresponding bwock of individuaw internaw stations, awwowing each of dem to be reached directwy from de pubwic switched tewephone network. In some of dese cases, a speciaw shorter diaw-in number can be used to reach an operator who can be asked for generaw information, e.g. hewp wooking up or connecting to internaw numbers. For exampwe, individuaw extensions at Universität des Saarwandes can be diawed directwy from outside via deir four-digit internaw extension +49-681-302-xxxx, whereas de university's officiaw main number is +49-681-302-0[15] (49 is de country code for Germany, 681 is de area code for Saarbrücken, 302 de prefix for de university).

Cawwers widin a private numbering pwan often diaw a trunk prefix to reach a nationaw or internationaw destination (outside wine) or to access a weased wine (or tie-wine) to anoder wocation widin de same enterprise. A warge manufacturer wif factories and offices in muwtipwe cities may use a prefix (such as '8') fowwowed by an internaw routing code to indicate a city or wocation, den an individuaw four- or five-digit extension number at de destination site. A common trunk prefix for an outside wine on Norf American systems is de digit 9, fowwowed by de outside destination number.

Additionaw diaw pwan customisations, such as singwe-digit access to a hotew front desk or room service from an individuaw room, are avaiwabwe at de sowe discretion of de PBX owner.